The invention relates to a method for sensorless detection of the position of a rotor of a mechanically switched direct-current motor, and a method for sensorless detection of the speed and/or the angle of rotation of a mechanically switched direct-current motor.
EP 0 689 054 A1, EP 0 730 156 A1 and DE 39 35 585 A1 all disclose methods for determining the speed and/or the distances in mechanically switched direct-current motors.
It is moreover generally known to determine, evaluate and utilise the alternating component of the current, the ripple, of direct-current motors as a measure for the speed of the motor.
DE 35 27 906 A1 describes for example a so-called zero crossing method, in which the zero crossings of the current are determined after elimination of the uniform component.
Also in DE 4217265 the ripple of the armature current signal is evaluated, with the relative maximal and minimal values being determined.
It is also known to describe the method of direct-current motors by means of an electromechanical motor status model based on the motor equations. The motor equation Uq(t)=c·F·n(t), also called generator equation, the motor equation Mm(t)=c1·F·Ia(t) and the electrical interrelationship Uq(t)=UM(t)−Ia(t)·Ra−L are likewise known.
The designations in the abovementioned equations mean in detail:                Uq the induced armature voltage;        c, c1, c2 the motor-specific variables, also known as motor constants,        F the magnetic flow,        n the speed,        ML the load torque,        Mm the motor torque and        MB the resulting acceleration moment,        Ia the motor or respectively armature current,        UM the motor terminal voltage,        Ra the armature resistance,        Rk the outer terminal resistance,        L the inductivity of the motor winding and        J the mass moment of inertia of the whole rotating arrangement including the parts to be moved.        
EP 0 689 054 A1 discloses a method and a device for speed measuring and detecting and signal preparation of the commutation current of a direct-current motor. The method provides a direct-current coupling of the motor via a measured resistance in the motor current circuit. The detected signal is amplified by an amplifier and further processed by means of a filter section and a second amplifier. The resulting signal of the current ripple is phase-shifted via a phase shifter and combined with the non-phase-shifted signal in an analog adder. The resulting output signal is the current ripple signal, which is excluded as speed-relevant with respect to its frequency.
The incremental determination of the speed from the commutation ripple of the armature current is likewise to be inferred from the essay “Unconventional speed measuring and adjusting in direct-current motors” by Birk, Elektronik 25, 14.12.1984, pp. 71 ff.
The basic problems of recognition and evaluation of the current ripple, in particular the sensitivity to interference in mains voltage and double commutations, are also to be inferred from these documents. Fluctuations in on-board mains voltage hamper the precision of evaluation, especially when this method is used in vehicles. The circuit expense necessary for comparing such interference is considerable with all compensation methods, however interference cannot ultimately be implied.
DE 197 29 238 A1 discloses a method for detecting the speed and/or the angle of rotation in mechanically switched direct-current motors. Measuring is complemented and controlled by a parallel working motor status model from the time sequence of the ripple of the motor current occurring in commutation. The electromechanical motor equations form the basis of the motor status model. A probable value of the current speed is extrapolated from the motor current and the motor voltage and a reliable nominal value range of the next commutation is determined. If no commutation moment is determined in the nominal value range, the extrapolated value is used. Otherwise the current speed is determined as accurately as possible from the commutation moment detected in the nominal value range. The motor-specific and load-dependent variable required for the motor status model can be firmly preset or can be adapted to the current speed in each case following detection of commutation procedures.
The aim of the invention is to provide a method for the most exact possible determining of the position of a rotor of a mechanically switched direct-current motor, and a method for sensorless detection of the speed and/or angle of rotation of a mechanically switched direct-current motor, which reduces the expense of compensation by influences of the mains voltage and improves the interference resistance.